Suggest u talk to O2 in England.
They have a package but you have to ask about it, which enables a uk user ring Ireland for little or nothing!! It's cheaper than me even ringing the UK landline to landline let alone landline to UK mobile if I was stuck with Eircom prices
I have both UK and Irish Sim cards and when in the relevent juristiction, I use the appropriate sim card and save myself heaps.
The bonus is that you could hang onto the sim card for other trips to the uK and be easily in contact at all times.
Good luck!